Expression of genes for ethylene biosynthesis, ethylene perception, and cell wall degradation in the fruit cortex and abscission zone was examined during fruit abscission and ripening in ‘Delicious’ apples (Malus × domestica). An autocatalytic burst of fruit ethylene production and accelerated fruit softening were associated with increased expression of genes related to ethylene biosynthesis (MdACS and MdACO), whereas reduced expression of ethylene receptor genes (MdETR and MdERS), increased expression of an ethylene signal transduction gene (MdCTR1), and increased expression of genes related to cell wall degradation (MdPG and MdEG) in the fruit cortex occurred during fruit ripening. Aminoethoxyvinylglycine (AVG) or 1−methylcyclopropene (1-MCP) inhibited fruit ethylene production, suppressed expression of MdACS1, MdACO1, MdERS1, and MdPG1 in the fruit cortex, and delayed fruit softening, whereas naphthaleneacetic acid (NAA) increased fruit ethylene production, increased expression of MdACS1, MdACO1, MdERS1 and MdPG1 in the fruit cortex, and accelerated fruit softening. Fruit abscission and expression of MdACS5A, MdACS5B, MdACO1, MdPG2, and MdEG1 in the fruit abscission zone were reduced by AVG and 1-MCP. NAA also reduced fruit abscission while reducing expression of MdPG2 and MdEG1 only in the fruit abscission zone. The levels of MdETR1, MdETR2, MdERS1, and MdERS2 transcripts in the fruit abscission zone decreased during fruit abscission and fruit ripening regardless of treatment. The combination of NAA and AVG was more effective in inhibiting expression of MdPG2 and MdEG1 in the fruit abscission zone and reducing fruit abscission than was either NAA or AVG used alone.

NAA and Ethylene Regulate Expression of Genes Related to Ethylene Biosynthesis, Perception, and Cell Wall Degradation During Fruit Abscission and Ripening in ‘Delicious’ Apples

Background and Aims:  Pre-veraison auxin treatments can delay grape berry ripening, but there is little information about their effects on berry development and wine composition. The aim of this study was to further investigate these effects and explore the practical implications of delaying ripening.



Methods and Results:  Treatment of pre-veraison Vitis vinifera L. cv. Shiraz berries with 1-naphthaleneacetic acid (NAA) significantly delayed ripening as measured by the accumulation of total soluble solids (TSS) and anthocyanins. The onset of the post-veraison phase of berry size increase was delayed in NAA-treated fruit, but these fruit were significantly larger than Control fruit at harvest. NAA-treatments significantly increased the synchronicity of berry sugar accumulation. GC-MS analysis of wine headspace volatiles showed significant, but largely small, differences in the concentration of 19 compounds. No significant difference in sensory properties was found between replicate small-scale wine lots made from Control and NAA-treated fruit.



Conclusions:  Auxin treatment delayed berry ripening, increased the synchronicity of sugar accumulation between berries, increased berry size and changed the levels of some volatile compounds, but did not affect wine sensory properties.



Significance of the Study:  We propose that NAA sprays might be used to delay grape berry ripening and increase the synchronicity of sugar accumulation, and therefore ripening, without deleterious effects on wine quality. This may be useful in controlling winery intake and fruit composition.

Auxin treatment of pre-veraison grape (Vitis vinifera L.) berries both delays ripening and increases the synchronicity of sugar accumulation

In plants, flowering is a crucial process for reproductive success and continuity of the species through time. Fruit production requires the perfect development of reproductive structures. Abscission, a natural process, can occur to facilitate shedding of no longer needed, infected, or damaged organs. If stress occurs during flower development, abscission can intervene at flower level, leading to reduced yield. Flower abscission is a highly regulated developmental process simultaneously influenced and activated in response to exogenous (changing environmental conditions, interactions with microorganisms) and endogenous (physiological modifications) stimuli. During climate change, plant communities will be more susceptible to environmental stresses, leading to increased flower and fruit abscission, and consequently a decrease in fruit yield. Understanding the impacts of stress on the reproductive phase is therefore critical for managing future agricultural productivity. Here, current knowledge on flower/fruit abscission is summarized by focusing specifically on effects of environmental stresses leading to this process in woody plants. Many of these stresses impair hormonal balance and/or carbohydrate metabolism, but the exact mechanisms are far from completely known. Hormones are the abscission effectors and the auxin/ethylene balance is of particular importance. The carbohydrate pathway is the result of complex regulatory processes involving the balance between photosynthesis and mobilization of reserves. Hormones and carbohydrates together participate in complex signal transduction systems, especially in response to stress. The available data are discussed in relation to reproductive organ development and the process of abscission.

Cross-talk between environmental stresses and plant metabolism during reproductive organ abscission

Fruit development is controlled by plant hormones, but the role of hormone interactions during fruit ripening is poorly understood. Interactions between ethylene and the auxin indole-3-acetic acid (IAA) are likely to be crucial during the ripening process, since both hormones have been shown to be implicated in the control of ripening in a range of different fruit species. Grapevine (Vitis vinifera L.) homologues of the TRYPTOPHAN AMINOTRANSFERASE RELATED (TAR) and YUCCA families, functioning in the only characterized pathway of auxin biosynthesis, were identified and the expression of several TAR genes was shown to be induced by the pre-ripening application of the ethylene-releasing compound Ethrel. The induction of TAR expression was accompanied by increased IAA and IAA-Asp concentrations, indicative of an upregulation of auxin biosynthesis and conjugation. Exposure of ex planta, pre-ripening berries to the ethylene biosynthesis inhibitor aminoethoxyvinylglycine resulted in decreased IAA and IAA-Asp concentrations. The delayed initiation of ripening observed in Ethrel-treated berries might therefore represent an indirect ethylene effect mediated by increased auxin concentrations. During berry development, the expression of three TAR genes and one YUCCA gene was upregulated at the time of ripening initiation and/or during ripening. This increase in auxin biosynthesis gene expression was preceded by high expression levels of the ethylene biosynthesis genes 1-aminocyclopropane-1-carboxylate synthase and 1-aminocyclopropane-1-carboxylate oxidase. In grape berries, members of both gene families involved in the two-step pathway of auxin biosynthesis are expressed, suggesting that IAA is produced through the combined action of TAR and YUCCA proteins in developing berries. The induction of TAR expression by Ethrel applications and the developmental expression patterns of auxin and ethylene biosynthesis genes indicate that elevated concentrations of ethylene prior to the initiation of ripening might lead to an increased production of IAA, suggesting a complex involvement of this auxin and its conjugates in grape berry ripening.

/pdf/interactions-between-ethylene-and-auxin-are-crucial-to-the-1ahplw0pio.pdf

Interactions between ethylene and auxin are crucial to the control of grape (Vitis vinifera L.) berry ripening.

Nine Gretchen Hagen (GH3) genes were identified in grapevine (Vitis vinifera L.) and six of these were predicted on the basis of protein sequence similarity to act as indole-3-acetic acid (IAA)-amido synthetases. The activity of these enzymes is thought to be important in controlling free IAA levels and one auxin-inducible grapevine GH3 protein, GH3-1, has previously been implicated in the berry ripening process. Ex planta assays showed that the expression of only one other GH3 gene, GH3-2, increased following the treatment of grape berries with auxinic compounds. One of these was the naturally occurring IAA and the other two were synthetic, α-naphthalene acetic acid (NAA) and benzothiazole-2-oxyacetic acid (BTOA). The determination of steady-state kinetic parameters for the recombinant GH3-1 and GH3-2 proteins revealed that both enzymes efficiently conjugated aspartic acid (Asp) to IAA and less well to NAA, while BTOA was a poor substrate. GH3-2 gene expression was induced by IAA treatment of pre-ripening berries with an associated increase in levels of IAA-Asp and a decrease in free IAA levels. This indicates that GH3-2 responded to excess auxin to maintain low levels of free IAA. Grape berry ripening was not affected by IAA application prior to veraison (ripening onset) but was considerably delayed by NAA and even more so by BTOA. The differential effects of the three auxinic compounds on berry ripening can therefore be explained by the induction and acyl substrate specificity of GH3-2. These results further indicate an important role for GH3 proteins in controlling auxin-related plant developmental processes.

/pdf/acyl-substrate-preferences-of-an-iaa-amido-synthetase-2jf52ujqgl.pdf

Acyl substrate preferences of an IAA-amido synthetase account for variations in grape (Vitis vinifera L.) berry ripening caused by different auxinic compounds indicating the importance of auxin conjugation in plant development

Effects of naphthaleneacetic acid (NAA), aminoethoxyvinylglycine (AVG), and 1-methylcyclopropene (1-MCP) alone or in combination on fruit ethylene production, preharvest fruit drop, fruit quality, and fruit maturation were examined in 'Golden Supreme' and 'Golden Delicious' apples (Malus ·domestica Borkh.). In 'Golden Supreme' apples, the combination of two applications of AVG and one application of NAA 3 and 1 week, respectively, before the anticipated optimum harvest date synergistically inhibited fruit ethylene production and delayed fruit drop and ripening. Compared with one or two applications of AVG, the combination of one application of AVG and two applications of NAA had much lower preharvest fruit drop, although there was no significant difference in fruit ethylene production among these treatments. In 'Golden Delicious' apples, 1-MCP at 396 mgL -1 had a better effect in delaying fruit drop than did AVG at 125 mgL -1 or NAA at 20 mgL -1 when they were applied a week before the optimum harvest date. The combination of NAA and 1-MCP or AVG was more effective in delaying fruit drop than were NAA, 1-MCP, or AVG alone. Fruit ethylene production was inhibited by 1-MCP and AVG but not by NAA. 1-MCP and AVG delayed fruit ripening, whereas NAA increased fruit ripening as determined by fruit firmness and starch.

/pdf/effects-of-naa-avg-and-1-mcp-on-ethylene-biosynthesis-4cb6em0ktk.pdf

Effects of NAA, AVG, and 1-MCP on Ethylene Biosynthesis, Preharvest Fruit Drop, Fruit Maturity, and Quality of ‘Golden Supreme’ and ‘Golden Delicious’ Apples

David H. Carbaugh

Papers

Effects of NAA, AVG, and 1-MCP on Ethylene Biosynthesis, Preharvest Fruit Drop, Fruit Maturity, and Quality of ‘Golden Supreme’ and ‘Golden Delicious’ Apples